Those of a more conservative bent point to early signs of dramatically extended survival. But whoever you ask, an experimental treatment known as immuno-oncology (IO) is the most exciting development in cancer care for years.

A small mountain of evidence is building for this once marginal area of cancer research. Nowhere was this clearer than at the annual jamboree for the great and good in cancer care, the American Society of Clinical Oncology (ASCO), where attendees last week were bowled over by a wealth of promising clinical trial results.

IO is set apart from other forms of cancer treatment because it harnesses the body’s natural defences to fight off tumours. The other approaches — chemotherapy, radiotherapy and surgery — bring in outside weapons, such as powerful drugs, high-energy radiation and scalpels.

Within five years, they hope to develop a test which can predict the danger of breast or ovarian concern for up to a decade ahead.

Experts said last night that the findings were a “promising” and exciting prospect, which could in future help protect women.

The study, by scientists at University College London, found that women who developed hereditary breast cancer, caused by a BRCA1 mutation, had the same changes to molecules in their blood as others who developed the disease despite having no genetic predisposition. The changes were found several years before diagnosis.

Almost 50,000 women a year are diagnosed with breast cancer in the U.K., and almost 12,000 die. According to the Canadian Breast Cancer Foundation, the disease continues to be the most common cancer diagnosis in Canadian women over the age of 20 — with one in four cancer diagnoses being breast cancer in 2013.

Around 10% of breast cancers are caused by BRCA1 and BRCA2 gene variants inherited from parents, but the rest are unexplained.

Until now there has been no reliable way to predict a likelihood of non-inherited breast cancer.

The “switch” discovered by scientists is part of a process that cause genes to be turned on or off. It is influenced by factors including alcohol and smoking, so women who knew they were more likely to develop breast cancer could adopt changes to their lifestyle, experts said.

The changes could be detected in blood samples years before symptoms develop, the study suggests.

Martin Widschwendter, the lead researcher, said: “We identified an epigenetic signature in women with a mutated BRCA1 gene that was linked to increased cancer risk and lower survival rates.

“Surprisingly, we found the same signature in large cohorts of women without the BRCA1 mutation and it was able to predict breast cancer risk several years before diagnosis.”

If the blood test revealed a woman was at higher risk, she ‘could then work with her doctor to explore the options available to help her take control of her own risk’

Dr. Matthew Lam, senior research officer at the charity Breakthrough Breast Cancer, said: “These results are definitely promising and we’re excited to learn how further research could build on these findings.”

He added: “This could mean that in the future a woman may be able to have a simple blood test to look for this DNA signature, and therefore know if she is at a higher risk of developing breast cancer. If she does have this signature, she could then work with her doctor to explore the options available to help her take control of her own risk.”

What proportion of women at higher risk of breast cancer have the epigenetic marker is unknown. The scientists analyzed blood sample DNA from 119 postmenopausal women who went on to develop breast cancer over a period of up to 12 years, and 122 who remained cancer-free.